Hydraulic circuit with valve to provide semi-float control of a dozer blade

ABSTRACT

There is disclosed a control circuit having a semi-float position for a bulldozer blade. The circuit includes selectively controllable check and relief valves operative to prevent the blade from dropping under the influence of gravity, but permits the blade to be moved under the influence of forces developed by a vehicle being pushed thereby.

United States Patent 1 Scheidt et a1.

HYDRAULIC CIRCUIT WITH VALVE TO Jan. 29, 1974 3,467,126 9/196 9 Ballard et a1. l37/596.l2 X PROVIDE SEMLFLOAT CONTROL OF A 3,472,127 10/ 1969 Scheidt 91/437 DOZER BLADE [75] Inventors: .gzrtiieitlijoslicgelfi; Robert W. White, Primary Examiner lrwin C. Cohen Attorney, Agent, or Firm-Freling E. Baker [73] Assignee: Caterpillar Tractor Co., Peoria, 111. [22] Filed: July 17,-1972 21 Appl. No.: 272,482

[57] ABSTRACT [52] US. Cl 172/801, 91/445, 91/447,

91/448 There 1s disclosed a control circuit having a semi-float [51] Int. Cl Eozf 3/76, E02f 3 /8 5, F15b 13/04 position for a bulldozer blade. The circuit includes se- 58] Field of Search 91/437 445, 446 447 448, lectively controllable check and relief valves operative 91/464 137/596 59632 to prevent the blade from dropping under the influl a 172/861 ence of gravity, but permits the blade to be moved under the influence of forces developed by a vehicle [5 6] References Cited being pushed thereby UNITED STATES PATENTS 3,127,688 4/1964 Hein et al. 91/445 X 8 Claims, 2 Drawing Figures zo zl i zZ M K l 14 F Z9 Z7 Z I Q) 26 L ./6 4 4/ F'Z R l v MAN |I lm 11 l L H e BACKGROUND OF THE INVENTION DETAILED DESCRIPTION OF PREFE RRED EMBODIMENT With reference now to the drawings and alternately The present invention relates to control circuits for 5 to G 1 and there iS diSClOSed in 2 dolflr bulldozers, and pertains particularly to a hydraulic blade positioning system having semi-float control means.

Bulldozers are commonly employed for pushing scrapers and the like to provide extra power during the loading cycle. When so employed, the blade ofthe bulldozer is raised and brought into engagement with a push block at the rear of the scraper vehicle. The normal hydraulic control system for blade control normally has provision for raise, lower hold, and float conditions.

If the blade is placed in the hold position, scraping action between the blade and pusher block will occur when scraper and tractor move over uneven terrain. This scraping action results in considerable undesirable wear on the dozer blade.

If the blade control is placed in the float condition after the blade contacts the push block, it will be free to follow the movement of the push block. However, should loss of contact occur between the blade and block, the blade will drop to the ground. This results in loss of loading time as the blade is again raised and brought into contact with the push block.

One proposed circuit for overcoming these problems is disclosed in my US. Pat. No. 3,472,l27, issued Oct. l4, 1969 and assigned to the assignee of the present invention.

The present invention offers a more simple and compact arrangement by eliminating a control lever, some hydraulic lines, and other elements.

SUMMARY OF THE INVENTION It is the primary object of the present invention to provide an improved hydraulic control circuit for a bulldozer blade that overcomes the above and other disadvantages of the prior art.

Another object of this invention is to provide a control circuit having means providing a semi-float condition for a dozer blade so that the blade is free to move upwardly and can be moved downward by a force slightly exceeding gravity. I

In accordance with the present invention, a control circuit for the control of a bulldozer blade includes an auxiliary circuit that provides a semi-float position. The semi'float position permits the blade to ride up and down with the engaging portion of a vehicle which is being pushed by-the bulldozer. The circuit in this position provides pressure adequate to prevent the blade from dropping under the force of gravity, but permits it to move under the influence of force between the vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS blade mounted in the usual manner on a tractor ll.

The vertical positioning of the blade 10 is controlled by means of a double acting hydraulic motor or jack 12.

The motor 12 is so mounted in the system that the rod end may be termed a raise end, and the head end may be termed a lower end because the powered direction of such end results in the specified function. Pressurized fluid for retracting and extending the jack 12 to respectively raise and lower the dozerblade is supplied from a suitable source comprising a pump 13, drawing fluid from a reservoir 14, where it is directed along a supply line 15 to a control valve 16. The control valve 16 is a four position control valve, with raise, hold, lower and float positions designated respectively by the letters R, H. L and F. The control valve 16 is operative in the raise and lower positions to alternately direct fluid to or from either the raise or lower ends of jack 12 by way of supply lines 17, 18 and Y19. A pair of make-up or anti-cavitation valves 20 and 21 are provided in the usual manner to provide for the drawing of make-up fluid from the sump or reservoir 14 when needed.

The raise side of the jack l2, supplied by fluid along supply lines 17 and 18, is further controlled by a check valve 22, the response of which is in turn controlled by a pair of relief valves 23 and 24.

The check valve 22 is of the type having a valve member 25 reciprocally disposed in a bore 26 of a housing, and operative to control flow of fluid between a pair of chambers 27 and 28 providing communication between lines 17 and 18. The valve member 25 also includes an orifice or restricted passage 29 communicating between chamber 28 and a control chamber 30. A spring 31 urges the valve member 25 into normally light seating engagement between thechambers 27 and I The check valve 22 is chiefly responsive to differential pressure existing between either of chambers 27 and 28 and the control chamber 30. The pressure within control chamber is chiefly determined by either one of relief valves 23 and 24, which are substantially identical in construction, but are responsive to different pressures. The check or relief valve 24, for example, contains a valve member 32 urged by means of a light spring 33 into seating or fluid flow blocking position. These relief valves are operative to control communication of fluid from the control chamber 30 by way of a conduit 34 and branch lines 35 and 36 with supply line 17. They are also operative to prevent fluid flow in the reverse direction. A suitable two-position control valve 37, having opened and closed positions respectively, such as, for example, a rotary valve as illustrated, is provided to control communication by way of line 34'between control chamber 30 and the low pressure relief valve 24.,

The control valve 37 is operatively connected by suitable linkage means comprising, for example, an arm 38 pivotally connected by means ofa link 39 to bell crank 40, which is connected by suitable lost motion means 41 to themain manual control valve 16. This connection permits the manual control valve 16 to be shifted between any one of raise, hold, or lower positions without affecting the setting of valve 37. However, movement of the control valve 16 to float position moves valve 37 to a position to cut off communication of control chamber 30 with low pressure relief valve 24.

OPERATION When the control valve 16 is in its hold position as shown, fluid flow by way of lines l7, l8 and 19 to or from either side ofjack 12 is completely blocked, with the result that the jack will maintain its selected positron.

With the control valve 16 shifted to the raise position, fluid from the pump 13 is-directed along line 17 into chamber 27 of valve 22, where it acts to move the valve member 25 downward to provide communication of fluid with line 18 and the rod or raise" end of the jack 12. in this position, the head end of the jack 12 is in open communication by line 19 with the reservoir or sump l4. l

When the valve is positioned in its lower position, pressurized fluid from pump 13 is directed by way of line 19 to head end of jack l2. Fluid in the rod or raise end of the jack 12 is communicated by way of line 18 with valve 22, where it then communicates by way of restriction or orifice 29 and line 34 with low pressure check valve 24. The valve 24 readily opens, permitting the escape of fluid from chamber 30, and the resultant opening of valve 22 so that fluid is then expelled from the rod end ofjack 12 along lines l8, l7

of jack 12 is in free, open communication by way of line 19 with the sump 14, so that the blade may be readily raised by an external force with little fluid resistance. On the other hand, relief valve 23 is of such a value that the weight of the bulldozer blade and accompanying linkage cannot generate sufficient pressure to open the valve solely as the result of forces generated by gravity. However, the setting of this valve is such that it will respond to external forces applied, such as might be applied when the blade is in contact with the push block of a scraper.

-From the above description, it is seen that there is disclosed a novel control circuit arrangement providing a semi-float condition for a bulldozer control system. The semi-float circuit is operative to hold a bulldozer blade in a raised" position against the forces of gravity, but is responsive to permit the blade to be moved with light forces slightly in excess of gravity in the upward direction, and in the downward direction only in response'to light forcesin addition to gravity. This arrangement permits the use of a bulldozer blade to freely follow the movement of the vehicle being pushed when travelling over rough terrain.

a double acting hydraulic jack, having a raise end and a lower end, operatively connected to raise and lower said bulldozer blade;

a source of pressurized fluid;

selector valve means operatively connected to selectively direct saidfluid to said raise and lower ends of the jack and including a float position;

a pressure responsive check valve including a pressure control chamber operatively positioned to control flow of fluid to and from said raise end of said jack;

means responsive to low pressure operative to relieve said control chamber;

means operatively connected to said selector valve means and responsive to movement thereof to the float position to render said means responsive to low pressure inoperative; and,

means responsive to high pressure operative to relieve said control chamber when said means responsive to low pressure is inoperative.

2. The control system of claim 1 wherein said means responsive to low pressure comprises a low pressure relief valve, and said means responsive to high pressure comprises a high pressure relief valve.

3. The control system of claim 2 wherein said means to render said low pressure valve inoperative comprises a rotary valve operative upon movement of said selector valve to the float position to block communication of said relief valve with said control chamber.

4. The control system of claim 3 comprising lost motion linkage means connecting said selector valve means to said rotary valve.

5. A hydraulic control system for controlling the vertical position ofa bulldozer blade. said system comprising:

a double acting hydraulic jackconnected to a bulldozer blade, said .jack having a raise end and a lower end;

a source of pressurized fluid;

selector valve means operatively connected to selectively direct said fluid to opposite ends of the jack and including a float position;

a pressure responsive check valve including a pres.- sure control chamber disposed to control flow of fluid from said raise end of said jack;

means responsive to low pressure operative to relieve saidcontrol chamber;

means operatively connected to said selector valve means and responsive to movement thereof to the float position to render said means responsive to low pressure inoperative; and,

means responsive to high pressure operative to relieve said control chamber when said means responsive to low pressure is inoperative.

6. The control system of claim 5 wherein said means responsive to low pressure comprises a low pressure relief valve, and said means responsive to high pressure comprises a high pressure relief valve.

7. The control system of claim 6 wherein said means responsive to movement of said selector valve comprises a rotary valve; and,

lost motion linkage means operatively connecting said rotary valve to said selector valve means.

8. The control system of claim 5 comprising lost motion linkage means operatively connecting said means responsive to movement of said selector valve means to said selector valve means. 

1. A hydraulic control system for raising and lowering a bulldozer blade, said system comprising: a bulldozer blade pivotally supported from a vehicle; a double acting hydraulic jack, having a raise end and a lower end, operatively connected to raise and lower said bulldozer blade; a source of pressurized fluid; selector valve means operatively connected to selectively direct said fluid to said raise and lower ends of the jack and including a float position; a pressure responsive check valve including a pressure control chamber operatively positioned to control flow of fluid to and from said raise end of said jack; means responsive to low pressure operative to relieve said control chamber; means operatively connected to said selector valve means and responsive to movement thereof to the float position to render said means responsive to low pressure inoperative; and, means responsive to high pressure operative to relieve said control chamber when said means responsive to low pressure is inoperative.
 2. The control system of claim 1 wherein said means responsive to low pressure comprises a low pressure relief valve, and said means responsive to high pressure comprises a high pressure relief valve.
 3. The control system of claim 2 wherein said means to render said low pressure valve inoperative comprises a rotary valve operative upon movement of said selector valve to the float position to block communication of said relief valve with said control chamber.
 4. The control system of claim 3 comprising lost motion linkage means connecting said selector valve means to said rotary valve.
 5. A hydraulic control system for controlling the vertical position of a bulldozer blade, said system comprising: a double acting hydraulic jack connected to a bulldozer blade, said jack having a raise end and a lower end; a source of pressurized fluid; selector valve means operatively connected to selectively direct said fluid to opposite ends of the jack and including a float position; a pressure responsive check valve including a pressure control chamber disposed to control flow of fluid from said raise end of said jack; means responsive to low pressure operative to relieve said control chamber; means operatively connected to said selector valve means and responsive to movement thereof to the float position to render said means responsive to low pressure inoperative; and, means responsive to high pressure operative to relieve said control chamber when said means responsive to low pressure is inoperative.
 6. The control system of claim 5 wherein said means responsive to low pressure comprises a low pressure relief valve, and said means responsive to high pressure comprises a high pressure relief valve.
 7. The control system of claim 6 wherein said means responsive to movement of said selector valve comprises a rotary valve; and, lost motion linkage means operatively connecting said rotary valve to said selector valve means.
 8. The control system of claim 5 comprising lost motion linkage means operatively connecting said means responsive to movement of said selector valve means to said selector valve means. 